1. Field of the Invention
The present invention relates to an internal combustion engine system control method and an internal combustion engine system, and more particularly to an internal combustion engine system control method and an internal combustion engine system, designed to automatically stop an internal combustion engine, upon satisfaction of a given automatic stop condition, and then automatically restart the internal combustion engine using an electric drive unit.
2. Description of the Background Art
In a control system for an internal combustion engine of a vehicle, there has been known one type designed to, upon satisfaction of a given automatic stop condition (i.e., condition for automatically stopping the internal combustion engine), automatically stop the internal combustion engine, and, upon satisfaction of a given restart condition after the internal combustion engine is automatically stopped, produce combustion of an air-fuel mixture in a stopped-state expansion-stroke cylinder which has been on an expansion stroke at least in an automatically stopped state of the internal combustion engine, so as to automatically restart the internal combustion engine, as disclosed, for example, in JP 2002-118978A (hereinafter referred to as ‘Document 1’). In such an internal combustion engine control system employing the above automatic stop/restart control scheme, it is necessary to use an electric drive unit for assisting start-up of the internal combustion engine, relatively frequently, i.e., every time the internal combustion engine is restarted. For this reason, the system disclosed in the Patent Document 1 employs a two-battery system comprising a general-purpose battery and a starter battery, wherein, depending on whether a type of internal combustion engine start-up process is a normal start-up process based on an operator's (driver's) manual operation (primarily, a manual operation of an ignition key switch) or an automatic restart process based on the automatic stop/restart control scheme, one of the two batteries is switchably used to improve an electric power supply capability.
Although the starter battery is generally specialized in supplying electric power to the electric drive unit to automatically restart the internal combustion engine in a state after being automatically stopped according to the automatic stop/restart control scheme, there are some cases where a user post-attaches an electric load, e.g., an accessory component, such as a lamp, to a terminal of the starter battery. In such cases, electric power stored in the starter battery is consumed in a stopped state of the internal combustion engine, and thereby the starter battery will fall into an overload state in which a total electric load exceeds an upper limit in design specifications. The use of the starter battery in the overload state is likely to cause a risk of being unable to ensure sufficient electric power during restart of the internal combustion engine.
It is contemplated to activate the electric drive unit with the support of the general-purpose battery when an amount of electric power stored in the starter battery is insufficient. However, some recent vehicles employ an electric load requiring electric power supply even in a stopped state of an internal combustion engine, such as a hill start assist system (hill holder), and thereby it is often the case that it is not easy to entirely cover required electric power by the general-purpose battery.